Contrast-Enhanced Ultrasound for Kidney Transplant

Overview

Contrast-enhanced ultrasound (CEUS) is a promising non-invasive imaging tool that may aid in the early detection of kidney transplant complications, such as delayed graft function (DGF) and acute allograft rejection. The technique uses an intravenous contrast agent to improve organ visualization with standard duplex ultrasound equipment. A number of FDA-approved agents, including Optison, Definity and Lumason are widely used to improve visualization in technically limited echocardiograms, and Lumason was recently approved for contrast-enhanced ultrasound of the liver. The specific aims of this study are to: develop, implement and refine a contrast-enhanced ultrasound protocol using Lumason to safely maximize kidney allograft visualization; determine associations between contrast-enhanced ultrasound and patterns of allograft injury consistent with delayed graft function; and to compare contrast-enhanced ultrasound with duplex ultrasound for differentiating acute rejection from other causes of dysfunction.

Kidney transplantation is the preferred treatment for end-stage renal disease (ESRD) given improved quality of life, longer survival and lower costs compared with chronic dialysis. Despite these long-term benefits, the first year post-transplant is a critical period that influences health care costs for transplantation and long-term patient and allograft survival. The two most common complications in the first year are delayed graft function (DGF), which affects nearly 25% of deceased-donor transplants, and acute allograft rejection, which affects nearly 10% of all transplants (deceased and living donor). DGF is most commonly caused by severe ischemia-reperfusion injury at transplantation and is a known risk factor for acute rejection and premature failure. Driven by an ever-growing transplant waiting list and limited organs, efforts to utilize higher-risk kidneys for increasingly higher-risk recipients may further increase these complication rates. While treatments exist for DGF and acute rejection, the current diagnostic paradigm is to obtain a duplex ultrasound (DUS) of the allograft, based on serial changes in serum creatinine, and then proceed to biopsy if there is clinical concern for rejection. Biopsy is the gold standard to differentiate between causes of allograft dysfunction, but the procedure is invasive and typically takes 24 hours or longer for an interpretation. Thus, early detection of these complications using non-invasive diagnostic methods (a major transplant research goal) could reduce our reliance on biopsies and help improve long-term patient and allograft survival. Researchers in the United States have safely performed contrast-enhanced ultrasounds of the kidney in healthy participants, and radiologists have used ultrasound contrast agents off-label to better visualize organs other than the heart when clinically indicated. In terms of kidney transplants, European data suggest CEUS of the allograft on post-operative day (POD) 7 is superior to DUS for predicting 12-month allograft function, but there are no published studies using CEUS on POD 1 to diagnose DGF or acute rejection. The pathophysiology of both DGF and acute rejection involve interactions between the microvasculature, parenchymal cells and inflammatory cells, though with differences in timing and within different zones of the kidney itself. A very important feature of CEUS is its capacity to measure microvascular perfusion, whereas DUS can only estimate flow within larger vessels. This potential innovation for assessing the renal macro- and microvasculature may allow for earlier non-invasive detection of DGF and acute rejection. With additional research, it may ultimately be shown that non-invasive CEUS will revolutionize early DGF and acute rejection diagnosis to enable improvement in long-term patient and allograft survival.